The first Index will find the value in the Max Count of cells (-2) in the array that are Numeric. Let's say it's column 6 = value 300.
The second Index does the same but without the "-2", so that's column 8 = value 200.

Those are two values that could be added with a "+". But the goal of this formula (it does work) is to SUM the range of values from column 6 to column 8.

This SUM command connects(?) the two Indexes with a ":" -- how does the formula know that means get all of the cells between the two index values?

Technically, INDEX always returns a cell reference. When you run INDEX "by itself", Excel simply converts that cell reference into that cell's value. When the context indicates that the INDEX result is the anchor point of a range, then Excel uses it to build that range.

Smart code -- it figures out what context you're using and then adjusts itself for that purpose. :-)
ciber -- I did try to evaluate what was going on and I knew I needed some secret knowledge for this.
Many thanks!!

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